Clinical pharmacology of dobutamine and dopamine in preterm neonates

Dobutamine is a b1 selective stimulant. b Receptor agonists are used to stimulate the rate and the force of cardiac contraction. The chronotropic effect is useful for the treatment of arrhythmias whereas the inotropic effect is useful to augment the myocardial contractility. Dobutamine is about four times as potent as dopamine in stimulating myocardial contractility in low concentrations and increases left ventricular output in the hypotensive preterm infants. Dobutamine possesses a center of asymmetry. The (2 )-isomer of dobutamine is a potent agonist of a1 receptors and is capable of causingmarked pressor responses. In contrast, (þ)-dobutamine is a potent a1 receptor antagonist which can block the effects of (2)-dobutamine. Dobutamine is relatively cardioselective at dosages used in clinical practice with its main action being on b1-adrenergic receptors. Dobutamine and dopamine undergo intense metabolism in neonates where they are conjugated with sulphate and O-methylated. The clearance and the half-life of dobutamine and dopamine range over one order of magnitude in neonates. Dopamine is widely used to increase blood pressure, cardiac output, urine output and peripheral perfusion in neonates with shock and cardiac failure. Dopamine is more effective than dobutamine in the short-term treatment of systemic hypotension in preterm infants. High doses of dopamine cause vasoconstriction, increase systemic vascular resistance, and, eventually, decrease renal blood flow. Treatment with dobutamine is associated with a significantly greater increase in left ventricular output in the single study reporting that outcome. Dobutamine is indicated for the short-term treatment of cardiac decompensation.